Central-station switching apparatus for automatic telephone systems.



P. A. LUNDQUIST & J. J. BROWNRIGG.

CENTRAL STATION SWITCHING APPARATUS EOE AUTOMATIC TELEPHONE SYSTEMS.

APPLICATION FILED MAY19,1903. 1,128,701 Patented Feb. 16,1915.

3 SHEETE- HEET 1.

F. A. LUNDQUIST & J. J. BROWNRIGG. CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS.

APPLICATION FILED MA'Y19. 1903.

1,128,701. Patented Feb. 16, 1915 8 SHEETS-SHEET 2,

F. A. LUNDQUIST & J. J. BROWNRIGG. CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS. APPLICATION FILED MAY 19, 1903.

1,128,701 Patented Feb. 16, 1915.

8 SHEETS-SHEET 3.

rfwezaz ozf' F. A. LUNDQUIST & J. J. BROWNRIGG.

CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS,

APPLICATION FILED MAY 19, 1903.

1,128,701 Patented Feb. 16, 191;,-

8 bHBElTS SHEET -3 662 fig (66 c5; Lzydwld wgia. 4%

F. A. LUNDQUIST & J. J. BROWNRIGG.

CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE msmms.

APPLICATION FILED MAY 19, 1903.

Patented Feb. 16, 1915 8 SHEETS-SHEET 5.

If. A. LUNDQUIST & J. J. BROWNRIGG. CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS.

APPLICATION FILED MAY 19. 1903.

1,128,701. Patented Feb. 16, 1915 8 SHEETS"SHEET 6.

F. A. LUNDQUIST & J. J. BROWNRlGG. CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS.

APPLICATION FILED MAY19,1903. 1,128,701 Patented Feb.16, 1915.

8 SHEETSSHEET 7. it x N \V ,4

III

n LLM din/666 66 fllrvzaezzfon:

5/, A A MW, 5; AM M7696 F. A. LUNDQUIST 8; J. J. BROWNRIGG. CENTRAL STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS.

Patented Feb. 16, 1915;

APPLICATION FILED MAY 19, 1903.

8 SHEETS-SHEET 8 UNITED STATES PATENT OFFICE.

FRANK A. LUNDQUIST AND JOHN BROWNRIGG, OF CHICAGO, ILLINOIS, ASSIGNORS, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

CENTRAL-STATION SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE SYSTEMS.

Application filed May 19, 190-3.

To all whom it may concern Be it known that we, FRANK A. Lonnoois'r and JOHN J. Bnowxaroc, citizens of the United States, residing at Chicag0,-1n

the county of Cook and State of Illinois,

The object of the invention is to simplify.

and improve the construction of switching apparatus at the central station for automatic telephone systems and to render the same ellicient in operation.

A further object of the invention is to provide a call bell at each subscribers station, all the call bells being operated from a main generator at the central station.

A further object of the invention is to provide means whereby when 21 called subscribers line is busy, the calling subscriber receives a busy signal, which does not disturb the called subscriber.

(lther objects of the invention will appear more fully hereinafter.

The invention consists substantially in the construction, combination, location and arrangement of parts. all as will be more fully hereinafter set forth, as shown in the a iii1)an \;'ing drawings, and finally pointed out in the appended claims.

Referring to the accompanying drawings, and to the various views and reference signs appearing tbereon,Figure 1 is a view in front elevation of a central station switching apparatus. embodying the principles of our invention. Fig. 2 is a view in side levation. looking from the left of Fig. 1. Fig. 3 is a view similar to Fig. 2, looking from the right-hand side of 1. Fig. 4 is a rear elevation. Fig. 5 is a top plan view showing the parts in the normal positions thereof. Fig. 6 is a. view similar to Fig. 5, showing the parts in actuated positions. Fig. 7 is a. view in horizontal section on the line 77. Fig. 3, looking in the direction. of the arrows. Fig. 8 is a brolqen detail view in section on the line 88. Fig. 4. looking in the direction of the arrows. Fig. 9 is a detached detail view in plan of the contact operating latch. Fig. 10 is Specification of Letters Patent.

Patented'Feb. 16, 1915.

Serial No. 157,798.

a similar view in side. elevation of the construction shown in Fig. 9. Fig. 11 is a view in diagram illustrating the application of the principles of our invention.

The same part is designated by the same reference sign wherever it occurs throughout the several views.

In automatic telephone systems as ordinarily installed circuit connections between the circuit wires of subscribers have been completed through a common conductor at the central station. circuit connection is to throw the entire system out of balance; that is, the pressure on one side of the telephone instruments is greater than the pressure on the other side. This is objectionable, for the reason that it frequently produces inductive crosstalk on adjacent lines. Another objection to this method of central station connection employing a common bus wire or conductor at the central station is that in the ease bf service wires or conductors of any considerable length the connection of such wires to the common conductor at the central station results, in edect, in grounding such conductor, thereby producing the same .ill effects of an unbalanced system.

It is one of the special purposes of our present invention to avoid this objection, and we accomplish this result by providing true metallic circuit conditions in which the total resistance in each of the legs of the metallic circuit is the same, thereby producing a balanced condition of the circuit. and preventing the inductive cross talk which .has been common heretofore in automatic telephone systems. In accomplishing this result we avoid the use of spools in series in the line circuits, and in place thereof we employ spools of high resistance bridged directly across the talking and ringing eircuit of the line wires. These spools of high resistance bridged directly across the line wires necessitate the use. of a higher voltage oi current for the proper operation of the system. but they produce a balanced condition in the line circuit. which prevents iuductional cross-talk. and also enables us to operate over lines of greater length. Moreover. in the operation of telephone systems employing low voltage of operating current, a current of high amperage is necessary. This is objectionable, for the. reason The result of such proper point results in a failure of the apparatus to properly operate.

Another feature of our invention is the employment of a central station generator for the signal device at the various subscribers stations employed in the system. The use of a generator at each subscribers station of sufiicient capacity to ring all the telephone call bells on the same line adds materially to the cost of an installation.

We avoid this objection by employing a central station generator for the entire sys tem, thus dis ensing with a separate generator at eac subscrihers station, thereby materially reducing the cost of installation, and thus permitting an increased number of subscribers to be supplied by each circuit, the number of subscribers on each line being limited only by the capacity of the cen tral station generator.

In securing a balanced condition in a complete metalhc circuit in accordance with the principles of our invention, We employ two pairs of'spools or coils of high resistance as a bridge across the two line "wires, said spools 0 high resistance being arranged in series-with each other, and a connection is'made. at a point between the two pairs of spools to one side of a battery or other source of current, the other side of such battery or source of current being grounded. This arrangement enables us to dispense with the third or common return or field wire, and this is a most important consideration as it results in greater economy in installation of the system.

In carrying out our invention, we bring the two wires of each subscribers line to the automatic switch at the central station, and arrange the terminal. of one of the Wires of each subscribers line in one system of contact points over which operates a contact arm, and the terminal of the other line wire of each subscribers line in another system of contact points, over which operates a cooperating contact arm. A convenient arrangement for carrying out this system is to arrange one series of contacts in a circle and the other system of line Wire terminal contacts in a concentric circle, and we mount the respective cooperating contact arms upon a rotatable shaft, said arms be ing conveniently arranged to extend diametrically opposite each other and radially from such shaft, and we provide a magnet controlled ratchet mechanism for imparting a step-by-step rotation to the shaft'carrying such arms, and a magnet controlled re lease mechanism for returning or restoring the contact arms to initial or normal position. The magnet spools which operate the ratchet mechanism of each switch mechanisrn at the central station constitute one of the pair of hi -h resistance coils employed in the bridge across the subscribers line wire, as above indicated. Of course, it is to be understood that a switching apparatus at central station as illustrated in the accompanying drawings, and as will be hereinafter more fully described in its details of mechanical construction and arrangement. is employed for each subscriber to the system. One of the line wires of the subscriber is led to one oi the contact arms of the switch apparatus corresponding to that subscribcrs line. and the other line wire of the subscriber is led to the other contact arm, and the various pairs of contacts over which said contact arms operate are in electrical connection. with the respective automatic switch at central station of the other subscribers to the system. The release of the ratchet mechanism is cflected by the energization of the'niagnet spools, the circuit of which is controlled by the joint or coincident closing of the circuit of the actu ating magnet and of a relay magnet, here inafter to be more particularly described; the relay magnet spools and the ratchet operating magnet spools employed in connection with each switch system comprising the two pairs of bridging spools across the line wire of the subscriber. Each switching apparatus is equipped with a magnet which controls the busy test.

' Generally, the foregoing explains the principles of operation of our invention, and While we have shown and will now describe one specific construction and arrangement of apparatus for carrying the principles of our invention into practical operation, we do not desire to be limited or restricted to the exact and specific details of construction and arrangement shown.

We will now describe a construction and arrangement of an automatic switch device at central station embodying the principles of our invention, which we haye found simple in construction and arrangement and efficient for the purposes desired.

Reference sign A designates a base, which in the form illustrated comprises a metallic ring, suitably counterhorcd on the under edge thereof, as i'nost clearly indicated in Fig. 8, to receive an insulating disk, B, in or through which are received the cooperating pairs of terminal contacts, indicated at C, D; C designating the outer ring of contacts, and D the inner ring of contacts. Each, insulating disk B contains one pair of contacts for each subscriber to the system, one member of each pair forming one of the outer circular series of contacts, and the other forming one of the inner series of contacts, and each coopcratingpair of contacts at each switch is connected electrically with the line wire of the corresponding sub scriber's line and silica the corresponding insulating disk B.

Rising form the base ring A, are,standards or uprights F forming supports for the operating parts of the ratchet mechanism, by which rotative movement is imparted to the ratchet mechanism through which shaft E is actuated, and also affording convenient means for attaching the switch mechanism to a'baseboard or other convenient support at the central station. Suitably supported upon the uprights F is a plate G, carrying centrally thereof a bearing, H (see Fig. '8), for shaft E. A spring J, 1s arranged to oppose the rotative movement of. shaft E, and normally exerts its tension in a direction to return or restore said shaft to initial position when said shaft has been rotarily displaced. Suitably connected to rotate with shaft E, are conductor-arms K, L, the conductor arm K operating over the series of contactsC contained 'in the outer circle or ring of contacts, and

the contact arm L operating over and in cooperation With the series of contacts D, forming the inner ring. The contact arm L is in electrical connection with shaft E, and through said shaft with the plate G, up rights F, base ring A, and the ratchet mechanism operating arm or armature presently to be referred to, these parts constituting what we will call the mass or base of the switch. The contact arm K, cooperating with the outer series or circle of contacts C, is suitably insulated from shaft E, as by means of an insulating disk M, mounted upon to rotate with said shaft. A convenient arrangement is shown for mounting the contact arm L upon to rotate with shaft E, wherein said arm is carried by an externally threaded split and slightly tapering sleeve N. adapted to be slipped upon. shaft E and to be clamped thereto by means of a nut O, 'asmost clearly shown in Fig. 8. Loosely sleeved upon shaft E, is'a ratchet disk P. This ratchet disk is provided with peripheral agatchet teeth. indicated at Q, with which cooperatesa spring pawl R, carried upon an arm S. suitably pivoted upon the plate G, and connected to the armature, T of the operating magnet spools A. A plate B, connected to but insulated from arm S. has connected thereto a retractile spring C, the tension of which may be adjusted in any suitable manner. as. for instance, by the rod I), said spring operating to retract th ar mature T, as soon as the circuit of magnet spools A"is opened. W hen the armature T is attracted by the energization ofmagnet spools A, an extension E of plate B makes contact'with a contact strip F, suitably insulated and connected up in circuit in a manner and for a purpose to be more fully described hereinafter. The arm S is provided with an extension or finger G, in electrical connection therewith, which when said armature is attracted by the energization of the magnet spools A, completes contact with contact point H, in a manner and for a purpose presently to be more fully described. The ratchet disk P is provided with crown ratchet teeth, indicated at J, upon the upper or peripheral edge thereof, with which engages a tooth or pawl K, down-turned from an engaging trip arm L, suitably fastened upon shaft E. This engaging trip arm may be mounted upon the shaft in any suitable or convenient manner. e have shown said arm mounted upon the shaft in a manner similar to the mounting above described for contact arm L, namely, by means of an exteriorily threaded split sleeve M (see Fig. 10), adapted to be slipped over shaft E and clamped thereon by means of a nut N, (see Fig. 8). In this manner the parts may be readily and quickly assembled and made up in quantity without regard to the nicety of machine Work, besides affording an efficient engaging or clamping relation between the shaft and the hub carrying the engaging trip arm. Engaged in a groove in the hub by means of which the engaging trip arm L is secured to the shaft E, is the end of an armature lever O, of tl e armature l of magnet spools Q. The magnet spools Q we designate the release magnets. The armature lever O is pivotally mounted upon'a trunnionat R, so that when the release magnet spools Q are energized, therebyattracting the armature P, the free end of armature lever- O is raised thereby through the engagement of the free end of said armature lever in the groove in the sleeve or hub of arm L, said sleeve is raised, thereby raising the shaft 1), and with it the contact arms K and L, and hence carrying the depending tooth K of engaging trip arm L out of engaging re lation with respect to the crown teeth J of disk P. and hence releasing the shaft, thereby returning or restoring the shaft to initial or normal position under the influence of tension or retracting spring J. A suitable stop S may serve toarrest the engaging trip arm L when the shaft E arrives at its initial position. Any suitable adjustable tension may be provided for returning or restoring the armature l and armature O to their initial positions. \Ve ha ve shown a simple arrangement, wherein a threaded rod is arranged to pass freely through said armature lever. and interposed between a thumb nut A threa .ed upon said rod and said lever, is a coiled spring B the tension of which is exerted in a direction to return or restore said armature lever to initial position as soon as the circuit of the release magnet spools QK is broken. If desired, a locking detent or pawl C may be arranged to engage the peripheral teeth of ratchet plate or disk I, to prevent reverse movement thereof. The ratchet pawl operating lever S is arranged to make electrical contact, as

at D (see Figs. 5 and 6) when said .actuating' lever is'returned or restored to initial position. The purpose and operation of this contact will be explained more fully hereinafter in connection with the circuit diagram, presently to be more fully explained.

Suitably mounted upon but insulated from the base ring or frame supporting said armature is prevented from being attractcd by the encrgization of the busy test magnets l, except when the ratchet operating magnets A are energized. In other words, the insulating finger l is arranged to extend underneath the free end of ratchet operating lever S, when the latter is in its normal retracted position, so that when said lever is in such position the energization of magnets l will be prevented from attracting the armature (:ibv reason of the finger J kangaging the under side of lever S. When, however. lever S has been actuated by the attraction of armature T, said lever is carried from engaging relation with respect to the insulated finger J and when in this position. the armature lcveror extension l-l'-' 'is free to be rocked, and the armature (i is free to be attracted when the circuit of the busy test magnets F 2 is completed. It, when the armature"Gl is attracted and the extensiori-H is held. in raised position, the armature T is released. the arm S again swings into the path of arm H and serves as a support therefor to prevent the latter from returning or being restored to initial or normalposition until after arm S has again been moved or actuated. In its raised position the extension H makes electrical contact with a contact spring K which places said contact spring K in electrical 'conncction with the frame E and when the armature G is released or restored to normal position, said armature makes electrical contact with a back-stop L the jrurd or connection M latter being insulated from auxiliary base E and being in suitable electrical connection with the insulated wiper contact arm K. as for instance, by means of the flexible Also, when arma tu eilever. G is in retracted or normal position, circuit is closed between insulated contact strips N, 0 (see Fig. 3) for a purpose and in a manner "presently to be more fully explained inconnection with the diagram.

Associated with the switch devices, as above described is a relay magnet, comprising the spools A mounted upon a frame B suitably insulated from the frame of the other mechanism of the switch. The armature C of the relay magnet is carried by an insulating block D suitably supported upon spring arms E E which form contacts cooperating withcontact points F, F F respectively, suitably supported and insulated from each other. The armature supporting insulating block D carries a metallic washer G which'is in electrical connection with the central supporting conductor contact spring E, and said washer is arranged to make'electrical contact with an insulated and adjustable back-stop H when the-armature C is retracted to initial or normal position. The spools of the relay magnets constitute one of the pair of bridging spools of the subscribers linct" wires, the coils of said spools being connected on one side to one of the subscribers line wires and on the other side to battery and also to the battery side of the pair of coils I scribers stations illustrated; K, K, K the call bells; L, L, L, the transmitters; M, V, M", the local batteries; N N, N the receiver hooks; these parts, together with the induction coils indicat e'd at O 0*, 0", being ofthe usual or any well known construction and arrangement, adapted when the receiver is removed from the hook to complete the local battery circuits as follows: from one side of the local battery, through wire (I. to. the receiver hook, wire 6, the primary (1 of the induction coil, wire 03, and the transmitter back to battery. lVe have described this circuit in connection with only one of the subscribers lines, but the same deeach subscribers station is arranged suit able means for throwing one or the other or both of the line wires to ground and for breaking the'circuit' of one orthe other or ieo both of the line wires with the apparatus at the subscribers station. Many specifically dili'erent constructions and arrangements may be employed for accomplishing these iesults, and as the specific construction and arrangement of such apparatus does not form part of the present invention, We have merely indicated diagrammatically suitable and operative means for accomplishing the desired result, wherein at each station is employed a pair of push-buttons, indicated at ll, 15.

We will describe the arrangement for only one of the subscribers, the arrangement being identical at each subscribers station.

The push-button 1 lcontrols .the contact of a contact spring 16 with one or the other of contacts 17, 18. The contact 17 is in electrical connection with the ground, as at P"; the push-button 15 controls a contact spring 19, which cotiperates with contact points 20, 21; the contact 20 being in electrical connection with the groundat P The contact 21 is in electrical connection through wire c with the receiver hook N, and the contact 18 is in electrical connection with the circuit of bell K and of receiver J. As above indicated, these parts are merely diagrann'natically indicated.

Q", It", designate the bank wires for the switch corresponding to one subscribers station, Q, R", the bank wires for the switch corresponding to another subscribers station, and. Q, R, the bank wires corresponding to the other subscribers station. The wire Q is connected through conductor f with thebase or mass of the corresponding subseribers central station switch, which is designated generally by reference sign A the mass including shaft E and operating arm h, to the insulated contact D ,'through wire y, contact thence to contact N when the circuit between 0 and N is closed, that is, when the circuit of the busy test armature is in its normal position; thence by wire ll, to line wire 13, thence through spring 19, contact'i l, wire 6, condenser D receiver hook N, wire L, bell K, contact 18, spring 16, wire 12. wire 22, to contact H of the relay magnet, thence to the middle spring E, wire 23, thence to the base of the busy test nagnet frame through the mass thereof to the armature G thereof, only' the armature being illustrated in the diagrammatic View; thence to contact strip L assuming the armature to be in its normal retracted position; thence through wire 24 to insulated wiper K.

n tracing the foregoing circuit we have disregarded the circuits of the bridging spools, and we have assumed that the contact wipers or arms L and K are in their normal positions, that is, said wipers or contact arms are not-in contact with an of the contaotsicarried by the insulating disk B,

The circuits of the bridging magnet spools will now be described. From wire it, the wire 25 is tapped, which leads through the spools A, whichare the operating magnets as above described, thence through wire 26 to the bus bar G which is a common battery strip at the central station; thence to one side of themain battery 11, the other side of said battery being connected to ground as at J. Similarly, the relay magnet coils A, are included in a circuit comprising a/ wire 27 tapped from wire 22, whence such cir cuit is completed through the spools A wire 28 to the bus bar tery H thence to ground' The circuit of the release magnet spools Q is traced follows: From the operating circuit wire 71,, through wire 29, insulated plate B, and extension E to contact strip F, wire 30, magnet spools Q, wire 31, contact spring E contact F thence through wire 32, to the battery bus bar G to battery H thence to ground at J. It will be observed that this circuit is normally open between extension E and strip F. It is normally openbetween contact strip E and contact F Consequently, in order to close the circuit of said release magnet spools Q, it is necessary to close the circuits thereof at both points through the energization of both the operating magnet spools A and the relay magnet spools A.

We will now trace the circuit of the busy test magnet F From one side of battery K", to busy buzz bus wire or conductor L thence through wire 33, busy magnet F through wire 34, to contact H, which contact is normally open but is closed, to the ratchet operating lever S, when the operat ing magnet A is energized, thence from ratchet operating lever S, rod E, and the mass to contact arm or wiper L. This circuit, of course, is not completed until the contact arm or wiper L has been actuated from its normal or retracted position, so as to be brought into electrical connection with a contact of the series of contacts I), but this circuit is com pleted coincidently with the making of corn tact between contact L and a contact of the inner series of contacts D. Ve will suppose that contact L has been brought into electrical contact with the first contact D. Thence the'busy test magnet circuit will be completed from contact arm or wiper L, through contact D and wire 35, to Wire Q which is the bank wire, to contact D at all of the switches B etc, but this circuit will be completed from bank wire Q only at that particular switch,

the mass of which is in electrical connection with said bank wire. Suppose',in the ease illustrated, this occurs at the switch indicated generally by reference Sign C, then said circuit will be completed through wire G and to the batwhich is common f, the shaft 'E, arm S, contact D wire g, contacts 0 N wire in through the operatingspools A at station C Wire 26, to main battery bus-bar G", to the other side of battery K". This circuit, of course, it will be understood is completed at each step imparted to contact arm L, this busy test circuit being completed successively through the various switches. For instance, when the wiper or. contact arm L is brought into contact with the first contact D, the circuit above traced is completed through that particular switch, the mass of which is in electrical connection with the corresponding bank wire. When the wiper arm L is advanced to the next contact, this busy test circuit is completed through that particular switch the mass of which is in electrical connection with that particular bank wire, and so on. Each of the pair of'spools A is of a definite and fixed resistance. In prac tice, we employ, say, 600 ohms resistance in each pair of spools. The actuation of armat-ure G of the busy test magnet when the magnet F is employed is opposed by a spring N", (see F igs. 3 and i) the tension of which is so adjusted that said armature will not be attracted when the current traversing the circuit of the busy test magnet is. required to overcome the 600 ohms resistance, above noted. When, however, say for instance, station B has called station C, or said stations are in communication with each other, then the'switcb arm or wiper L of station B is in electrical contact with the first of the series of contacts D. In that event, when station A seeks to call C the circuit of the busy test magnet F will be divided, part going through wire 35 at sta tion B, thence through switch arm or wiper L at that station, which under the condition assumed is in contact with the first of the series of contacts D; thence through the shaft E, ratchet actuating arm S, and the mass at station B, back 'stop D and on as above described, traversing the same path at B as has been describe above with reference to the path at switch C, thence back to the batter bus-bar G, to the other side of battery 18 and the other path of said circuit traversing the same circuit as abovg described, with reference to the switch a C, back to battery bus-bar G, and to battery K". This results in dividing the circuit of the busy test magnet at station A into two parts or branches, each containing 600 ohms resistance, namely, each branch circuit including therein the coils of the actuating magnets A at the two respective stations B3, C. The result of this 1s to reduce the available resistance in this circuit to 300 ohms, and when the resistance of this circuit is so reduced, the tension ofspring N will be overcome, allowing the armature of the busy test magnet F at the calling cuit on one side of the line.

station A pto be attracted. As above described, this armature will not be attracted until the ratchet actuating arm S has been moved out of the way or path of the finger J of the armature arm, When the ratchet operating lever S has been moved out of the path of this finger, the armature G of the busy test magnet will be permitted to roclr and thereafter the release of the ratchet actuating arm S will cause said lever to form a support for the finger J thereby holding the busy test magnet armature G in attracted position. The attraction of this armature opens the circuit between contact L and armature G thus .opening the cir- The same movement also breaks the circuit between contact strips 0 and N thereby opening the other side ofithe line. This movement also closes the following circuit: from one side of bat tcry K, to battery bus'bar L", wire 37, buzzer 38, wire 39, to contact strip K contact strip H, armature G wire 28, contact strip E back-stop H wire 22, relay magnet A wire 2-8, bushel? G, to the other side of the battery K. This completes the metallic circuit for the buzzer, The disturbance created by this buzzer is thrown back through the receiver at the station making the call through a circuit tapped from wire 22, as follows: wire 12-, strip 16, contact 18, receiver J the secondary of the induction coil, contacbM, receiver hook N, which under the conditions named is raised, the receiver J having been removed from such book; thence through condenser D wire 6, contact 21, strip 19, wire 13, wire it, wire 25, magnet A, wire 26, to battery bus-bar G, to the other side of the battery K". This gives the subscriber at station A, who is attempting to make a call, the busy 0L) buzzing sound in his receiver, notifying him that the line he is seeking to call busy. v

WVe have in the foregoing description referred to the presence of a condenser I) in 11 0 the local circuit connections of each telephone. -()ne purpose of these condensers is to prevent the circuit of the busy test magnot from being completed it would otherwise be through the telephone at each subscribers station, thereby preventing the our rent of the busytest from finding the desired resistance in its path.

We will now describe the central station generator for the ringing circuits of the en- 12o tire system, which in connection with an automatic telephone system we regard as novel and important.

Reference Sign O designates the central station ringing generator common to the entire system. his generator may be of any convenient type or form. One side of this generator is connected through wire 40, con: denser i1, and wire 42, which is a bank wire, that is, is common to all of the central station switches. At each switch this wire 4-2 is tapped oif or is in electrical connection with contact point F of the relay. From the other side of the generator 0- leads a tact F", and breaking electrical connection between contact H and strip E. The breaking of electrical connection between the last two contacts prevents the ringing circuit from bein completed through the telephone oi the subscriber making the call. We will now trace the generator circuit through the switch A", assuming the relay magnets A to have been energized. This circuit is completed from the generator 0*, through wire it), condenser 41, wire 42, to contact F strip It. wire 44. wire it, contact strips N 0'. w ire {7, contact D ratchet armature lever S, shaft 19. and the base of contact wiper or arm L, thence to the particular line in connection with which the wiper arm L has been actuated, thence to the switch corre: sponding to the subscriber being called, thence back to the contact arm or wiper K of the calling subscriber, wire 24, strip L armature (t wit-e23. strip E, contact F, to the opposite side of the generator.

Having row described the mechanical coir strut-tion and arrangement of the switching apparatus, and having also traced the various viii-nits involved-in the electrical operation of the apparatus, we will now explain the operation of making and receiving a call, assuming that the apparatus at each station is at normal.

Now suppose the subscriber corresponding' to switch A desires to call the subscriber of switch (77. The first operation is to remove the receiver J at station corresponding to switch A from the receiver hook. thereby breaking connection between the receiver hook N and the local signal bell circuit K of the calling station and completing the local receiver circuit and also the local transmitter circuit at the calling station. The circuit from the ground at 1 to the line wire 1? is then made and broken a given number of times corresponding to the number of the station to be called; for instance, it the station of switch C is the station to be called, the circuit connection from line wire 13 to ground at P is made and broken once, station of switch C being, the station corresponding to number one of the system. As above explained, the making and breaking of this circuit may be effected in any suitable or convenient manner; aiid ,as we have explained, we have merely shown an illustrative make and break device for accomplishing this result and comprising the push-button 15, spring 19, and contact 20, this merely for the purpose of illustrating the operation of the apparatus \Ve will now trace the circuit thus made and broken: from ground at P, through contact 20, spring 19, wire 13, wire it. wire 25, magnet A, wire 26, battery busbar G battery H to ground at J. The single completion of the circuit of the magnets A imparts a single actuation to armature and ratchet operating lever S, thereby imparting one step of rotative movement to the ratchet disk P, hence rotativclydisplac ing shaft E, and with it the conductor or wiper arms L and K, so as to bring said wiper arms into cooperative and contacting relation with respect to'the cooperating pairs of contacts C D, constituting the first pair from normal on the disk B of switch A. This places the telephoi 3 at station corresponding with switch A in electrical. communication with the telephone of statior C. The next step is for the subscriber at sta tion A to ring the signal bell at station 1 This is accompli hed by completing the circuit between line and the ground at the calling station, that is, at station A. The completion of this circuit may be effected in any convenient manner; -As illustrative of an operative arrangement, the subscriber at A pushes button 14, thereby bringing contact strip 16 into electrical connection with contact 17. Thereupon the ringing circuit is completed, follows: from ground at P contact 17, strip 16, wire 12, wire 27, relay magnet A, wire 128, battery bus-bar G, battery H to ground at J. The comple- 7 tion of this circuit energizes the relay mag-. not A causing the armature thereof to 110 be attracted, thereby completing the ringing circuit from the central station generator 0 as follows: through wire 40, condenser 41, wire 12, contact F, strip E wire 4%, wire it, contacts N 0 wire g, contact D lever S, shaft 1* and mass or base, contact arm or wiper L, the first of the contacts D, wire 35.- wire (1", wire f at switch C shaft E, armature b, and mass, as above explained at switch C through contact. D, wire 9, strip strip N wireit, wire 13, strip 19, contact 21, conductor 6, condenser I), receiver hook N, wire at station C bell K at station C contact 13, spring 16, wire 12, wire 50, to bank wire It, then back to the calling station or switch A. to wire 51, Contact arm or wiper K, wire 21, strip L armature G, of the busy test magnet, wire 221, spring E, which under the conditions mentioned has been drawn down by the energization of relay A. at switch A thence ta wmm F to the oppositesidr; sf the It 15] be obgerwd than tum thu return mrmntabow mined sin.- weii mciudes mum tn the return bank wire, mus :Lulir I out the appamius sf the SWHfih, A sLniiu return connection is arrangvd at emrh 1;; swilic This cfiwts nging n1" s: at station C from station 'rmwever, the station at (F then upun completion of line 13, to groun i I at station V the subscriber at tatin A making the (53 W 1 x'scaive in his race the busy m2 as ming tE simian C 1 5 been calied 01" ism ccmmlm fan with the subscriber at si tm'z B ditinns mesaficsiafi am: mmm

L K at Suzi-"h H l): um cm 1932;;

1': mini Avie these can; cuit, F" the out haw: herein-(thaw 1' branches. one through aha (mil?- k at switch B and 411:: the Wuating (rails A a the z'vsistancc of each pan of iLcsv mugwt (rni. is 600 ohms the total efi'v "1w wflisumrv in i external circuit uf H1? bi imam; ,T m" switch A2 will be 360 ohms. uni 5'" tin: Kermit)?! 0i Petr-(willy spring KR (my Hm aim-action of armature A of tha' flew magnet F at statizm M muting said armature m 1w:

d magnet 811 5mm im" V, m- Lmn 09b: "Pips L" :n m: (rand also 51mm wt witcl'i The npenin opus both of f' um of 1% m1 S's-fiber A as; he calling 5 through the of he fiery 38, W13, I. H" unnufmx; 1? mm: H, Wire l.v u'agmm :1 mvmiiiic flimulii;

tin-magi) the miegauozm nmljing tn switch if US 11% Wire 12% n: h, Qirips; N", 0 wire I, cant- D'f, armature S, shaftii, and ma 5, contact arm or \vi 'mr L, wire f return bank wire (5, to a ire 3;), tbs first, :z-f 1 1$ (Joni/a D m. :gwitvh A" wniavt mm or wiper L, 121% ii, swarmnuw; 1w. and mzw to contactwiwcon tact fips A wire k to wire 11:), i hvnce zhs'r Hm :phom at the station of Hm miiing Aftw cummunicatiw ted the parts may be H Mix alarm 271 121W fiimpie m conveni- WHY f 2* ins awe, and in the m1; '3 7 TiW madam m :zmwkmm g mind wire 13 to is? P" 1 in (M ii! iriz'wii of Ian-1g" fi. to imtmzv an: fix-mini the A? hemeen contact exienmmn 5"" and the rezsuli of a:i=. sing f lming: at P ii: in do -z: the a uymt (3011s A" rim gin line and battery to gz-ourd, wmpiaring Ara-nit between ins [1119? these {1am ions .nrm'iiwr iguana? 11ml and thv mmnwi. parts,

im im win 4 ".2: "*2 i .qwietexy bah'mi metallic cirun: may thereby avoiding the objection of inductive cross-talk, wherein we are enabled to secure an eiiicient return busy buzz or test at a calling station in case a called station is already in operation or is bu: v, and wherein we provide a system capable of being applied to lines of long distance, it being evident that the principles of our invention may be carried out to a system of indefinite capacity, depending, merely upon the capacity of the central station calling generator.

In the application of this invention to party lines, oneor more telephones may be ridged across the line wires 12, 13 or 12", 13*, or 12*, 13".

It is obvious that many variations and changes in the details of construction and arrangement would readily occur to persons skilled in the art and still fall within the spirit and scope of our invention. \Ve do not desire, therefore, to be limited or restricted to the exact details shown and described; But

Having now set forth the object and nature of our invention, and a construction embodying the principles thereof, What we claim as new and useful and of our own invention, and desire to secure by Letters Patent of the United States, is:

1. In a telephone system, a central station, subscribers lines terminating thereat, a switch for connecting said lines, a busy test magnet associated with said switch, resistance coils associated with said lines, means whereby when a connection is completed from one subscriber's line to another a resistance coil is included in the circuit of said busy test magnet to prevent actuation thereof, and means whereby when the called line is busy the circuit of the busy test magnet is divided into two branches each including a resistance coil whereby the effective resistance in the circuit of the magnet is reduced and said magnet is actuated.

2. In an automatic telephone system, a central source of ringing current, a switching mechanism corresponding to each subscribers station and including a busy test magnet, a resistance coil at each switching mechanism, means whereby when one subscriber completes the calling circuit to another subscribers station the coil of the called subscriber is included in the circuit of said busy test magnet to prevent actuation of such magnet, and means whereby in case the called subscribers line is already busy the circuit of said busy test magnet is divided into two branches, each. includin a coil, thereby reducing the effective resistance in the circuit of the busy test magnet of the calling subscribers switching mechanism and hence actuating the latter.

3. In an automatic telephone system, a central source of ringing current, a switchmg mechanism corresponding to each subscriber and controllable from the subscribers stations, each switching mechanism including a busy test magnet and a resistance coil, means for completing the calling circuit between the switching mechanism of each subscriber to the switching mechanism of each of the other subscribers to the system, v aid means operating to include the resistance coil of the called subscriber in circuit with the busy test magnet of the calling subscriber, thereby preventing operation of such bisy test magnet, and cans whereby when the called subscribers line is busy the circuit of the busy test magnet of the calling subscriber is divided, each part thereof including a coil of each of the two subscribers in communication with each other, thereby reducing the total effective resistance in the circuit of the busy test magnet of the calling subscriber to permit the latter to operate to give a busy test signal to the calling subscriber.

4. In an automatic telephone system, a plurality of subscribers stations, a busy buzzer for said stations and an automatic exchange having operating magnets, a bus .bar of raised electric potential at the exchange, a second bus bar of higher electric potential, means for bridging said bus bars through the busy buzzer to any subscribers station, and means for grounding said first named bus bar through either line wire of any desired subscriber, said grounding establishing circuits through the operating magnets of the exchange for the said subscriber.

5. In an asthmatic telephone system, a plurality of s ,oscribers stations, a busy buzzer for said stations and an automatic exchange having operating magnets, a bus bar of raised electric potential at the ex-. change, a second bus bar of higher electric potential, means for bridging said bus bars through the busy buzzer to any subscribers station, means for grounding said first named bus bar through either line wire of any desired subscriber, said grounding establishing circuits through the operating magnets of the exchange for the said subscriber, and means whereby the simultaneous energization of said magnets actuates a return of the exchange apparatus to normal condition.

6. In an automatic telephone system, a switching mechanism corresponding to each subscriber and controlled from the subscribers stations, each switching mechanism 111- eluding a busy test magnet and a resistance coil, means forcompleting the calling cireuit between the switching mechanism of each subscriber and the switching mechai nism of each of the other subscribers of the system, said means operating to include the resistance coil of the called subscriber in circuit with the busy test magnet of the calling'subscriber, whereby the busy test magnet will not receive operating current, and

5 means whereby when the called subscribers line is busy the resistance coils of the two subscribers in communication with each a other are placed in parallel connection with the busy test ma )0 scriber, whereby t at of the calling subsaid busy magnet will receive operating current to give a busy test signal to the calling subscriber.

In witness whereof, we have hereunto set our hands this 12th day of May 1903, in the presence of the subscribing witnesses.

FRANK A. LUN DQUIST. JOHN J. BROWNRIGG. Witnesses:

CHAS. H. SEEM, S. E. DARBY. 

